I haven't dropped Lambda yet, I've just been focusing on Bang cause I'm most familiar with him. I think Hakumen will teach me defense as well, and I like long normals. I did well with Lambda at times cause I was forced to be defensive at times. Bang makes me kinda reckless but nonetheless a good character for me because a good defense with Bang only strengthens his potential. It also teaches me that even though I'm a rushdown character I have to be smarter, and I'm not always gonna have the chance to be in somebody's face (which is why I struggle against Rachel cause I'm impatient as hell sometimes).
Also in terms of Lumin and Valk, one and a half mistakes against him and you're already dead. Seriously though, don't get hit.